• respecting the Injlexion of Li^ht, 151 
1, M. Fresnel found that the fringes formed by inflexion 
may be examined by an eye-glass, without receiving them upon 
a white surface ; and by adapting a micrometer to the eye-glass, 
he was able to determine their breadths, even to the one or 
two-hundredth part of a millimetre. 
2. By following the external fringes to their origin, by means 
of a lens with a short locus, he perceived the third fringe at the 
distance of less than the one-hundredth of a millimetre from 
the edge of the inflecting body. 
B. The inflexion of the passing light is influenced by the dis- 
tance of the radiating or luminous point from the inflecting 
body, as appears from the following results. 
Distance of ‘the radiating 
point from the body. 
Distance behind the 
body whei-e the 
inflexion was mea- 
sured. 
Angular deviation 
or inflexion of 
the red rays of 
the first fringe. 
12 ' 6 ^' 
3 55 
100 millimetres. 1 metre. 
6 metres. 1 metre. 
Hence it follows, that the ray kiffers a less degree of in- 
flexion in proportion to the distance from which it diverges. 
4. When the inflexion of the same fringe is measured at dif- 
ferent distances behind the inflecting body, the distance of the 
radiant point remaining the same, it is found to be different at 
different distances ; and hence it follows, that the successive po- 
sitions of the same fringe are not in a straight line^ hut form a 
curve^ whose concavity is turned towards the infecting body. 
The lines which join the different positions of the fringe of -all 
the orders of colours, are hyperbolas, having for their common 
foci the radiating point and the edge of the inflecting body. 
In some of M. rresnefs experiments, the sagitta of curvature 
was about 1 millimetre, or the 25th part of an inch, which is 
nearly 50 times greater than the error of observation. 
5. M. Fresnel measured the fringes produced by various bo- 
dies, and found, by accurate measurement, that they all pro- 
duced the same inflexion, the back of a razor giving tlie same 
fringes as its sharp edge. 
Results of a similar kind were obtained by Dr Brewster in two 
sets of experiments, one of which was made in 1798, and the 
other in 1812 and 1813. He compared the fringes formed by 
gold-leaf, with those made by masses of gold ; those formed by 
films which produced the colours of thin plates, witli those 
